Method of fabricating an array of multi-electroded piezoelectric transducers for piezoelectric diaphragm structures

ABSTRACT

A circuit provides energy to a plurality of piezoelectric diaphragm structures formed in a two-dimensional array. Each piezoelectric diaphragm structure includes a piezoelectric element in operational contact with at least a first side electrode and a second side electrode. A switching system includes a first connection for a first power source, for application of power to the first side electrode and a second connection for a second power source, for application of power to the second side electrode. In a first state, power appropriate for performing a poling operation of the piezoelectric material is available for application to the first electrode, and the second electrode, and in a second state, power appropriate to activate the piezoelectric material to cause operational movement of the poled piezoelectric diaphragm structure is available for application to the first electrode and the second electrode.

BACKGROUND

The present application is directed to piezoelectric diaphragmstructures, and more particularly to poling systems for polingpiezoelectric diaphragm structures for optimized diaphragm displacement.

Piezoelectric diaphragm structures are implemented as actuators whichmove upon being supplied with electrical energy, and as sensors (e.g.,pressure, movement, strain sensors) where diaphragm movement istranslated into electrical signals. One particular implementation of adiaphragm structure is as part of an ejection unit used to eject dropssuch as ink, biofluid or other material from a fluid reservoir.

In configuring a piezoelectric diaphragm structure, the ferroelectricceramics are poled in order to exhibit the piezoelectric characteristicsrequired for operation. Prior to a poling operation, domains of thematerials are randomly oriented. During poling, an intense electricfield is applied, which may vary dependant on the implementation, butmay be in a range of 200 to greater than 15,000 V per millimeter andpreferably 1,000 V to 15,000 V. When the field is removed, electricdipoles of the material stay roughly but not completely in alignment.This operation provides the material with a residual polarization.

Presently, such poling operations may occur during fabrication ofpiezoelectric diaphragm structures. In one operation, the piezoelectricmaterial is poled with an external circuit which is temporarily attachedduring the manufacturing process. Therefore, the poling operation occursonce, and only during the manufacturing process.

A drawback to this accepted procedure is that over time a piezoelectricmaterial will degrade. This may occur when operation of thepiezoelectric diaphragm structures exceed the mechanical, thermal and/orelectrical limits of the material, as well as through natural aging.This degrading of the material is particularly acute when highlyresponsive piezoelectric materials are used. Such highly responsivepiezoelectric materials are known to improve the amount of displacementwhich may be obtained by a diaphragm structure. However, high responsematerials will also tend to degrade quicker than other piezoelectricmaterials. In consideration of the above, it is appreciated that once adiaphragm structure is incorporated into a larger device, such as a dropejection unit, overtime the operational capabilities of the largerdevices may degrade due to the decrease or loss in the polingdirectionality of the piezoelectric material.

The present state of the art does not address this potential degradationof the diaphragm structure in devices that are operating on site in anenvironment such as an office building, home, factory or other enduser's location.

SUMMARY

A circuit provides energy to a plurality of piezoelectric diaphragmstructures formed in a two-dimensional array. Each piezoelectricdiaphragm structure includes a piezoelectric element in operationalcontact with at least a first side electrode and a second sideelectrode. A switching system includes a first connection for a firstpower source, for application of power to the first side electrode and asecond connection for a second power source, for application of power tothe second side electrode. In a first state, power appropriate forperforming a poling operation of the piezoelectric material is availablefor application to the first electrode, and the second electrode, and ina second state, power appropriate to activate the piezoelectric materialto cause operational movement of the poled piezoelectric diaphragmstructure is available for application to the first electrode and thesecond electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual drawing showing a piezoelectric ejection unitwhich may implement a diaphragm structure of the present application;

FIGS. 2A and 2B, respectively, illustrate a disc diaphragm structure inaccordance with the present application;

FIGS. 3A and 3B illustrate an annular ring diaphragm structure inaccordance with the present application;

FIGS. 4A and 4B illustrate a two-region diaphragm structure inaccordance with the present application;

FIGS. 5A and 5B, respectively, show a partial cross-sectional view and apartial top view of the annular ring diaphragm structure;

FIGS. 6A and 6B are, respectively, partial cross-sectional and partialtop views of an annular ring diaphragm structure without centerelectrodes;

FIGS. 7A and 7B are, respectively, partial cross-sectional and top viewsof a two-region diaphragm structure;

FIGS. 8A and 8B illustrate an oxide mesa design which may be used toconnect to electrodes of each of the diaphragm structure embodiments;

FIG. 9A identifies directions of the axes of poling directions in aconventional co-ordinate system;

FIG. 9B identifies directions of the axes of poling directions in acylindrical coordinate system.

FIG. 10A illustrates a partial view of an inter-digitated electrodearrangement in a parallel piezoelectric expansion state;

FIGS. 10B and 10C show a diaphragm structure in a concave position;

FIG. 11A illustrates a partial view of an inter-digitated electrodearrangement in an anti-parallel piezoelectric contraction state;

FIGS. 11B and 11C show a diaphragm structure in a convex position;

FIG. 12 is a chart presenting the results of a diaphragm displacementlapping study;

FIG. 13 is a chart representing a diaphragm displacement study for adisc piezoelectric;

FIG. 14 illustrates a diaphragm displacement study for an annular ringpiezoelectric;

FIG. 15 is a partial side view of diaphragm displacement in accordancewith parameters of FIG. 10B;

FIG. 16 is a chart containing the results of diaphragm shapes formed dueto relative electrode width (i.e., duty cycle) variations;

FIG. 17 presents a curve illustrating, an optimal piezoelectricthickness;

FIG. 18 illustrates the results of a volume displacement lapping studyfor various underlap and overlap positions;

FIG. 19 depicts a partial view of an optimized annular ring diaphragmstructure in accordance with the present application;

FIG. 20 is a chart illustrating the results of deflection for atwo-region diaphragm structure; and

FIG. 21 is a chart depicting an optimum boundary point for a two-regiondiaphragm structure according to the present application.

FIGS. 22A-22B show a top and side views of a diaphragm structure inaccordance with the present concepts;

FIGS. 23A-23D are investigated options of the application of E-fields tothe diaphragm structures in accordance with the present concepts;

FIG. 24 is a partial side view of a diaphragm displacement for option22A above;

FIG. 25 is an alternative view of FIG. 24 showing the voltagepenetration into the piezoelectric;

FIG. 26 illustrates the poling directions of the disc and annular ring,as well as the E-field direction of the disc in preparation for thevarious options of voltage applications to the annular ring such as inFIG. 23;

FIG. 27 presents a set of curves illustrating various applications ofvoltages to the outer electrodes of the annular ring; and

FIG. 28 depicts a bimorph structure which may be used in accordance withthe present application.

FIG. 29 shows a bottom metal electrode and conductor configuration;

FIG. 30 is a top view of piezoelectric island and interconnect, carryinga top side electrode and conductor configuration;

FIG. 31 shows the components of FIGS. 29 and 30 carried on a printhead.

FIG. 32 is a drive circuit which permits poling and drop ejectionoperations;

FIG. 33 is a high level process flow for piezoelectric elementproduction and direct bonding to a final target substrate or system;

FIG. 34 illustrates a piezoelectric element array on a top surface of acarrier substrate;

FIGS. 35A and 35B show alternative embodiments of a piezoelectricelement array deposited with electrodes and other thin film metals forbonding, the piezoelectric element array is on a top surface of acarrier substrate;

FIG. 36A illustrates an embodiment of a bonding of piezoelectric filmsto a final target which is conductive using a thin, nonconductive epoxybonding containing sub-μm (micrometer) conductive balls;

FIG. 36B shows a nonconductive epoxy bonding process;

FIG. 36C is an enlarged view of a section of FIG. 36B;

FIG. 37 illustrates a bonding of piezoelectric films to a final targetusing thin film intermetallic transient liquid phase bonding;

FIG. 38A illustrates radiation of a beam through the carrier substrateduring a liftoff process;

FIG. 38B depicts a heat transfer for the liftoff process;

FIGS. 39A and 39B are alternative designs of bonding the thick filmarray to a final target substrate or system or to a transfer substrate,for poling operation; and

FIG. 40 is a high level process flow for piezoelectric elementproduction including attachment of the piezoelectric elements to atransfer substrate prior to transfer to a final target substrate orsystem.

DETAILED DESCRIPTION

The following description primarily emphasizes the use of a diaphragmstructure as an actuator, wherein electric signals are provided to thediaphragm structure, causing movement. It is to be appreciated, however,the descriptions set forth herein are equally applicable to the use of adiaphragm structure as a sensor. In this design the diaphragm structureis used to generate output signals whereby the pressure or otherphysical environmental actions imposed on the diaphragm structure aresensed and delivered to an external source.

FIG. 1 illustrates a conceptual drawing showing a piezoelectric ejectiondevice 10, which includes a plate 12 having two parallel surfaces 14,16. The plate may be made from a metal, and anisotropically etched orotherwise manufactured to provide a recess 18 therein. Alternatively,plate 12 may be a silicon, glass or ceramic laminate where recess 18 isprovided by an appropriate process, including, for example, by etching,molding or laser ablation. The recess 18 has a bottom surface 20 whichis substantially parallel to plate surface 14, in order to form arelatively thin membrane for use as a diaphragm 22. Alternatively, thediaphragm may be a separate plate which is laminated or attached to theplate 12 after recess 18 is formed.

The recess bottom surface and thus the surface area of the diaphragm ispredetermined to permit the appropriate deformation. Bottom surface 20has a piezoelectric material 24 built, deposited or otherwise attached.An electrode 26 is positioned on a surface of the piezoelectric material24, and is connected to a source of energy 28 such as a power supply. Anozzle plate 30 is formed on plate surface 14 and has an internal cavity32, open against the plate surface and aligned with the diaphragm 22, toact as a fluid reservoir. The nozzle plate 30 has a nozzle 34 which maybe centrally aligned with the diaphragm 22 or may be offset asappropriate. Cavity 32 is filled with fluid 36 through an inlet (notshown).

Actuation of energy source 28, causes energy, such as in the form ofvoltage, to be applied to piezoelectric material 24 via electrode 26,which in turn deforms the diaphragm 22 in the upward direction towardsnozzle 34, as shown in dashed line. This action increases the pressureon fluid 36 in cavity 32, initiating the ejection process. A droplet 38is ejected from nozzle 34 as diaphragm 22 moves upward. The diaphragmthen moves in a direction away from the nozzle, as when voltage isremoved from electrode 26.

Turning to FIGS. 2A-4B, illustrated are three circular piezoelectricdisc diaphragm structures in accordance with the present application. Itis to be understood that the diaphragm structures in this and otherembodiments, are described with particular reference to a substantiallycircular design. However, such a description is only intended for easeof explanation and is not intended to limit the embodiments to circulardesigns. Rather, the disclosed concepts are equally applicable to othergeometric shapes, such as but not limited to rectangular, diamond,rhombus. In these instances, the structures would therefore have acentral region (i.e., equating to a disc) or an outer edge region (i.e.,equating to an annulus).

FIGS. 2A and 2B, are top and side views of a disc piezoelectricdiaphragm structure 40, which includes a diaphragm 42 having anappropriate stiffness for an intended use, such as but not limited tostainless steel.

Diaphragm 42 is covered by a piezoelectric disc 44. As shown in FIGS. 2Aand 2B, the piezoelectric disc 44 may overlap diaphragm 42. While notillustrated in this figure, diaphragm 42 may be part of a largerstructure, such as plate 12 of FIG. 1. Therefore, the overlappingpiezoelectric disc 44 would cover a portion of such a plate, clamp oranchor-type structure. As shown more clearly in FIG. 2B, piezoelectricdisc 44 has attached to a first or top surface an electrode arrangement,such as an inter-digitated electrode grid 46, comprised of a pluralityof electrodes 46 a-46 c. Although not shown in this figure, discdiaphragm structure 40 may also include either a single electrode ormultiple electrodes on a second or bottom surface of piezoelectric disc44. In one implementation, block 47 is a power supply which driveselectrodes 46 a-46 c, causing a deformation of piezoelectric disc 44,which in turn causes movement of diaphragm 42. In this implementation,the disc diaphragm structure 40 is used as an actuator. In analternative implementation, disc diaphragm structure 40 may be designedas a sensor, where physical movement of diaphragm 42 causes movement ofpiezoelectric disc 44, which in turn generates electrical signals. Inthis embodiment, block 47 is a device which receives the electricalsignals from electrodes 46 a-46 c.

Turning to FIGS. 3A and 3B, illustrated is an piezoelectric annulardiaphragm structure 48 in accordance with a second embodiment of thepresent application. In this design, diaphragm 42 is covered by apiezoelectric annular ring 49, having an outer radius 49 a, and an innerradius 49 b. The inner radius 49 b is a distance from the center of thediaphragm 42, whereby an inner area of diaphragm 42 is not covered bythe piezoelectric annular ring 49.

As shown in FIG. 3B, a plurality of electrodes 46 a′, 46 b′ of anelectrode arrangement, such as an inter-digitated electrode grid 46′ areon a first or upper surface of annular ring 49. Since there is nopiezoelectric material at the inner area of diaphragm 42, electrode 46 cof FIG. 2B is not used. Also, similar to FIG. 2B, this device may beoperated either as an actuator, or a sensor, similar to that describedabove.

Turning to FIGS. 4A and 4B, set forth is a piezoelectric two-regiondiaphragm structure 50 in accordance with a third embodiment of thepresent application. Two-region diaphragm structure 50, includes apiezoelectric annular ring region 51 and a piezoelectric disc region 52separated by boundary 53. These regions are concentric and are attachedto diaphragm 42, which, similar to the previous embodiment, may be madeof any material having appropriate stiffness for an intended use, suchas but not limited to stainless steel, similar to FIGS. 2A-3B.

An upper surface of annular ring region 51 carries a first electrode 54a, and upper surface of disc region 52 carries a second electrode 54 b,which form an electrode arrangement. Similar to FIGS. 2B and 3B, block47 may represent a power source or a signal receiving device, dependantupon whether the two-region diaphragm structure 50 is operational as anactuator or sensor.

Turning to the partial cross-sectional view of FIG. 5A and partial topview of FIG. 5B, a more detailed discussion is provided for circularpiezoelectric disc 44, of disc diaphragm structure 40, which carries afirst inter-digitated electrode (IDE) grid 56 on a first or top surface,and an optional second inter-digitated electrode (IDE) grid 58 on asecond or bottom surface. The numbering of electrodes of FIG. 2B (i.e.,46 a-46 c) is replaced in the present discussion with new numbering forconvenience of explanation. Diaphragm 42, on which piezoelectric disc 44is located, is part of a larger component such as plate 12 of FIG. 1, orother appropriate design. In this arrangement diaphragm 42 is held byclamp or anchor section 60. Diaphragm 42 and clamp or anchor section 60may be formed as a single integrated body, or these sections may beindividual components fastened together by known techniques.Piezoelectric disc 44 may overlap diaphragm 42 and extend onto theanchor 60.

Inter-digitated electrode (IDE) 56, includes a plurality of electrodes62 a-62 b, and electrodes 64 a-64 c. Electrodes 62 a-62 b and 64 a-64 care circular in construction, to correspond with the circularpiezoelectric material. In practice, electrodes 62 a-62 b have appliedvoltages of an opposite sign of electrode 64 a-64 c. In an alternativedesign, optional IDE 58 may be replaced with a single electrode.

FIG. 5B, which is a top view of IDE 56, also shows electrical conductors70 a, 70 b used to provide energy to electrodes 62 a-62 b and 64 a-64 c.Electrodes 64 a-64 c are connected to a first conductor 70 a. Thesupplied electrodes 62 a-62 b are shown with gaps not touching conductor70 a. A similar design is used in connection with second conductor 70 b.Conductors 70 a and 70 b may be provided in the Z-axis perpendicular tothe electrodes.

FIGS. 6A and 6B, are partial cross-sectional and top views of annularring diaphragm structure 48. In this design, since the center ofdiaphragm 42 is not covered with piezoelectric material, middleelectrode 64 a is not used. The remaining electrodes and other numberedelements are the same as shown in FIGS. 5A and 5B. As will be expandedon in following sections, removal of the center portion of thepiezoelectric material will, in some driving arrangements, permitincreased movement of the piezoelectric annular ring 49, resulting ingreater diaphragm deflection.

FIGS. 7A and 7B are partial cross-sectional and top views of two-regiondiaphragm structure 50. In addition to electrode 54 a on a top surfaceof annular ring 51, and electrode 54 b on a top surface of disc 52, anelectrode 54 c may be located on a bottom surface across both theannular ring region 51 and disc region 52. FIG. 7B shows the annularring electrode 54 a connected to conductor 70 a, and disc electrode 54 bconnected to conductor 70 b. These conductors are provided to a powersource configuration (not shown) which drives the independentelectrodes. In this embodiment, the entire diaphragm is covered withpiezoelectric material, therefore, the stiffness of the diaphragm ismaintained to a greater degree than diaphragm structures presentlyavailable, which tend to locate the edge of the piezoelectric materialclose to the edge of the active diaphragm, or somewhat interior. Thoseexisting designs cause the stiffness of the diaphragm to be reduced atthe edge of the active region, which affects the overall diaphragmstiffness. In FIGS. 5A, 6A and 7A the piezoelectric material 44 mayextend beyond the diaphragm 42, thus further increasing the stiffness.The increased stiffness afforded by the diaphragm structures in thesefigures improve performance in fluid-ejecting applications, as theresonance frequencies will be maintained at a higher level.

As previously mentioned, each of the foregoing embodiments may haveconductors 70 a and 70 b provided in the Z-axis perpendicular to theelectrodes. It is to be appreciated, however, that other connectionschemes may be used. One such alternative is, for example, shown byFIGS. 8A and 8B. This design employs an oxide mesa 71 to which theelectrodes of piezoelectric material are attached. Grooves 71 a, 71 bare formed in mesa 71 from approximately an area corresponding to thecenter of the mesa to the edge of the mesa. Metal lines 71 c and 71 dare patterned or deposited within grooves 71 a, 71 b, providing externalconnections. The metal lines 71 c, 71 d in the grooves are selectivelycovered by an overcoat oxide 71 e, such that metal which corresponds toelectrodes, remains exposed. Then when placed into contact with thediaphragm structures (e.g., 40, 48, 50) appropriate connections to theelectrodes are made. A similar connection to electrode 54 c of FIG. 7Aor array 58 of FIG. 5A may also be made.

Turning to the manufacture of the piezoelectric diaphragm structures, astage of manufacture includes poling of the piezoelectric material. Dueto the anisotropic nature of piezoelectric material, effects aredependant upon direction. Therefore, as depicted in FIG. 9A, to identifydirections in one design, the axes or directions, termed 1, 2 and 3, areintroduced, analogous to X, Y and Z of the classical right-handorthogonal coordinate system. The axes 4, 5 and 6 identify rotations(i.e., shear). In another design, and as will be explained in moredetail below, the convention of direction described in FIG. 9A isaltered or rotated to a position such as shown in FIG. 9B. In thiscoordinate system, the reference directions are provided in what may beconsidered a cylindrical coordinate system, where direction 1 is in theZ-axis, direction 3 is now in a radial in-plane direction, and direction2 is designated as a θ position, representing the cylindrical aspect ofthe coordinate system. FIG. 9B is intended to emphasize an alternativepolarization mode which will be expanded on below.

The poling process uses relatively high voltages to obtain the requiredapplied field, creating the possibility of dielectric breakdown underthe high applied field. Therefore, an objective of the poling process isto provide a maximum amount of reorientation of the piezoelectricdomains using the lowest applied field in the shortest possible time. Anumber of poling techniques, including DC poling, DC plus AC poling, aswell as pulse or switched DC poling, have been described, and any ofthese or other appropriate poling techniques may be used. These polingtechniques may be implemented with elevated temperatures to facilitatethe poling operations.

Once the piezoelectric material has been poled, application of anelectric field (E-field) will displace the piezoelectric. Thisdisplacement of the poled piezoelectric is primarily a function of theapplied electric field strength (E), the piezoelectric used, and thelength (L) of the piezoelectric. The material properties can bedescribed by the piezoelectric strain coefficients d_(ij), whichdescribe the relationship between the applied electrical field and themechanical strain produced.

The most common mode of operation is a d₃₁ mode which applies whenpolarization of the piezoelectric is in direction 3 of the classicorthogonal coordinate system—where the electric field points in thedirection 3 (i.e., FIG. 9A)—and the strain is in the 1 axis (i.e.,orthogonal to the polarization axis). An alternative mode of operation,which has been considered by the inventors is a d₃₃ mode, which occurswhen polarization is in direction 3 of the cylindrical coordinatesystem—where the electric field points in the direction 3 (i.e., FIG.9B)—and the strain (deflection) is along the same axis. Thus, operationin the d₃₁ mode (with reference to FIG. 9A) will include havingpolarization in the Z-axis (direction 3) extending out of thepiezoelectric material, where the E-field will be applied in the Z-axis(direction 3). On the other hand, operation in the d₃₃ mode reflects thecoordinate system shown in FIG. 9B, where, the poling direction is inthe R (radial) axis (direction 3) with the applied E-field also being indirection 3.

In the d₃₁ mode, applying the E-field in direction 3 at a first polaritycauses the piezoelectric to expand, and reversing the polarity causescontraction.

In the d₃₃ mode, when the generated E-fields are parallel to the polingdirection, the design is in a parallel state, and the piezoelectric willexpand. When an expanding piezoelectric is built on or otherwiseattached to a diaphragm, the expansion of the piezoelectric causesbending motion of the diaphragm, thereby resulting in the overallstructure moving to a convex position when observed from thepiezoelectric side. Contraction of the piezoelectric will occur when theE-field is anti-parallel the poling direction, which pulls in thepiezoelectric, causing a counter bending reaction in the diaphragm,resulting in movement to a concave position. Thus, in the two-regiondiaphragm structure such as structures 40 and 50, actuation of the firstarea causes a length change in the Radial direction and actuation of thesecond area causes a length change in the Radial direction of anopposite sign of the first area.

In the embodiments of FIGS. 2A, 2B, 3A, 3B, 5A, 5B and 6A, 6B, both thepolarization axis and the applied electric field are applied in theplane of the piezoelectric along the R-axis. Thus, operation is in a d₃₃mode, as mode d₃₃ applies when the electric field is along thepolarization axis (direction 3) and the strain (deflection) is measuredalong the same axis. The common mode of operation for existing diaphragmstructures is to operate in a d₃₁ mode which applies when thepolarization and the E-field are in the Z-direction as before, but thestrain is in the 1 axis (i.e., orthogonal to the polarization axis).FIGS. 4A and 4B operate in this manner.

To illustrate operation in the d₃₃ mode, attention is directed to FIG.10A, which shows a partial view of inter-digitated electrode arrangement(IDE) 56 carried on a piezoelectric (e.g., 44 or 49) where the mode ofactuation is the d₃₃ mode, i.e., both the poling and E-field arein-plane with the piezoelectric and pointed in the R-axis direction.This design, makes it possible to take advantage of the transversechanges in geometry obtained in the d₃₃ mode, which are two to threetimes larger than the transverse changes available in the d₃₁ mode, formost piezoelectric materials. The preceding concepts may also beapplicable to the two-region diaphragm structure 50. However, as thatembodiment does not use an IDE (with a plurality of electrodes) thefigures would be slightly different.

In FIG. 10A, the poled direction is illustrated by arrows 72, which aregenerally or at least partially in-plane with the piezoelectric. Thegenerated E-fields are shown by arrows 74, which are parallel to thearrows representing poling direction 72. When in a parallel state, thepiezoelectric will expand when voltage is applied to the electrodes ofIDE 56.

When an expanding piezoelectric is built on or otherwise attached to adiaphragm, the expansion of the piezoelectric causes bending of thediaphragm. The convex region near the clamp 60 causes more motion thanthe region in the center, thus forcing the center region downward andforcing a concave shape near the center.

This concept is illustrated more particularly in connection with FIGS.10B and 10C. In FIG. 10B, base or clamp 60 holds one end of diaphragm42, which carries piezoelectric material (e.g., 44 or 49). As previouslymentioned, operation is in the d₃₃ mode as E-fields are formed byapplication of voltage to electrodes (e.g., 62, 64), the piezoelectricmaterial begins to expand, causing the thickness of the inter-electroderegions 80 to grow thinner. This pushes electrodes 62, 64, forming ascalloped top surface as shown in FIG. 10C. It is noted that FIG. 10C isexaggerated for explanation purposes.

With continuing attention to FIG. 10B, the depth of the applied positive76 and negative 78 voltages into the piezoelectric (e.g., 44 or 49) arevisually illustrated. In this embodiment, the value of the appliedvoltage ranges from +3 volts to −3 volts.

Turning to FIG. 11A, shown is inter-digitated electrode (IDE)configuration 56, such as in FIG. 10A, except that the applied E-field82 is anti-parallel to the poled direction 72. This arrangement resultsin a contraction of the piezoelectric (e.g., 44 or 49). As depicted inFIGS. 11B and 11C, contraction of the piezoelectric results in theinter-electrode regions 86 to bulge above electrodes 62 and 64. Thiscontraction pulls in the piezoelectric, causing a counter bendingreaction in diaphragm 42, resulting in movement to a concave position inthe region near the clamp.

Thus, when E-fields are applied parallel to and in-plane with the polingdirection, the piezoelectric expands causing the inter-electrode regionsto stretch sideways, pulling in the surface to conserve volume andleaving the electrode regions to form small protrusions. Forcontraction, the E-fields are in-plane with and anti-parallel to thepoling direction, causing the inter-electrode regions to contractsideways, pushing out the surface, and leaving the electrode regions toform depressions.

The foregoing has described diaphragm structures which provideimprovements over existing diaphragm structures by implementing acircular diaphragm with inter-digitated or two electrode control, wherethe applied E-field is in-plane with the poling direction, such that thediaphragm structure operates in a d₃₃ mode. The described diaphragmstructures may be operated as a piezoelectric disc design or apiezoelectric annular ring design.

The performance of the described diaphragm structures depends on severalfactors, including: the pitch (p) of the electrodes, the electrode dutycycle (w/p—i.e., width-to-pitch ratio), the resulting penetration of theE-field, and the nominal E-field strength. For efficient usage, thepitch is maximized while minimizing electrode duty cycle for any levelof E-field strength. The piezoelectric effect is a volumetric responsethat is dependent on the penetration of E-fields into the piezoelectric.The depth of penetration depends on a ratio between the pitch (p) topiezoelectric thickness (t_(PZT)) (i.e., p/t_(PZT))which, as will bedescribed, has been determined to be approximately 5 for a practicalimplementation using a single-sided IDE design. As noted, a second IDEmay be added to an opposite surface of the piezoelectric to improve thepiezoelectric effect. In comparison to the d₃₁ mode traditionally usedin parallel plate electrode (PPE) configurations, in the d₃₃ mode thebias voltage scales only with the electrode pitch, not the piezoelectricthickness.

The chart of FIG. 12 presents the results of a finite element simulationof a piezoelectric on stainless steel diaphragm related to diaphragmdisplacement and the effects of overlapping and underlapping between thepiezoelectric and the diaphragm, (i.e., r_(PZT)/r_(Diap)). The studyused the following specifications: Diaphragm radius (r_(Diap))=0.5 mm(500 μm), Piezoelectric thickness (t_(PZT))=20 μm, Diaphragm thickness(t_(Diap))=35 μm, height (h)=2.5 μm, Electrical field (E)=3V/μm, Pitch(p)=100 μm, and Duty cycle (dc)=10%.

The simulation investigated a variety of scenarios where a 500 μmcircular diaphragm was actuated by circular piezoelectric discs rangingfrom 100 μm to 700 μm in diameter. The developed curves 100-112 areplotted to reflect the diaphragm displacement (nm) in accordance with aradial distance from the center of the diaphragm (mm). Curves 100-112show the transition of the diaphragm shape, which has a positivedisplacement for piezoelectric discs with smaller radii, and rapidlyevolves into negative displacements for piezoelectric discs havinglarger radii, e.g., from 400 μm (0.8 underlap) to 700 μm (1.4 overlap).Curve 100 shows no deflection, since there was only one electrode on thepiezoelectric.

Curve 112 represents a situation where the radius of the piezoelectric(r_(PZT))=700 μm, whereas the radius of the diaphragm (r_(Diap)) is 500μm, resulting in a 200 μm overlap. Measured at the center of thediaphragm, the displacement is over −600 nm as shown by curve 112. Thus,the largest diaphragm displacement in this study occurs when r_(PZT)=700μm. The displacement characteristics of the remaining curves may beunderstood from the foregoing discussion.

Attention is now directed to comparing the diaphragm displacementefficiency between a disc diaphragm structure 40 and an annular ringdiaphragm structure 48. Turning to FIGS. 13 and 14, illustrated arecharts plotting the results of finite element simulations of diaphragmdisplacement (nm) based on the radial distance from the center of thediaphragm (mm) for the disc structure and the annular ring structure.These charts compare three different inter-digitated electrodearrangements, where electrodes are on top of the piezoelectric (IDE 1)114, 122, electrodes on top and bottom of the piezoelectric (IDE 2) 116,124, and electrodes on the bottom of the piezoelectric (IDE 3) 118, 126.Each chart also plots a curve for a system implementing a known parallelplate electrode (PPE) design 120,128. In this study, the followingparameters were used: t_(PZT)=20 μm, r_(Diap)=0.5 mm (500 μm),t_(Diap)=38 μm, r_(PZT)=0.5 mm (500 μm), p=25 μm, dc=20% and E≈3V/μm.

The results of this study confirm for both structures that thedouble-sided (IDE2) design provides the largest displacement. In FIG. 13the diaphragm displacement for the IDE2 disc design is about −300 nm,according to curve 116. Due to the radial inward compression experiencedby the actuated piezoelectric, displacement is constrained when thecenter of the disc thickens due to radial stress. To improve thisperformance, a small circular piezoelectric portion is removed at thecenter of the diaphragm for stress relief so that the piezoelectric canexpand. With, for example, a 100 μm piezoelectric portion removed fromthe center, and the resulting annular ring structure subjected to thesame driving conditions as for the disc structure, the IDE2 curve 124shows a displacement of about −440 μm. The dip on the left of the PPEcurve 128, is due to the loss of the piezoelectric material at thecenter.

With continuing attention to annular ring structure 48, FIG. 15 is apartial side view of diaphragm displacement in accordance with theparameters of FIG. 14 having IDE 56 only on the top surface ofpiezoelectric annular ring 49, which is driven in a parallel expansiond₃₃ mode.

The chart of FIG. 16 contains a set of curves 130-146 for the annularpiezoelectric diaphragm structure 48, such as partially depicted in FIG.15. The curves define diaphragm displacement (nm) versus the radialdistance from the center of the diaphragm over a plurality of dutycycles (i.e., where the duty cycle is considered to be the width topitch ratio (w/p)) ranging from 10% to 90%. The diaphragm displacement,and therefore volume displacement variation, is monotonic over thevarying duty cycles. The lower duty cycles (e.g., 10%) generate thegreatest negative diaphragm displacement as shown by curve 146.

Understanding the benefits of overlapping/underlapping of thepiezoelectric, the use of IDEs, and the characteristics of a disc versusan annular ring in a diaphragm structure operating in a d33 mode,further finite element simulations at various underlapping oroverlapping values were performed to determine optimal diaphragmstructures. TABLE 1 provides some results of the simulations, as plottedin FIG. 12, for the listed specifications where an IDE is located onlyon the top surface. The study increased the size of the piezoelectric(r_(PZT)) in 50 μm steps. TABLE 1 IDE1 (d₃₃) “Lap” Studies r_(Diap) =0.5 mm, t_(PZT) = 20 μm, t_(Diap) = 38 μm, E ≈ 3 V/μm, p = 100 μm, dc =10% overlap r_(PZT) r_(PZT)/ U_(max) ΔV Cv Case (um) r_(diap) (nm) (pL)(pL/V) UNDER 100 0.20 4.89 0.33 0.0012 150 0.30 3.21 3.73 0.0138 2000.40 44.82 18.09 0.0670 250 0.50 54.62 23.69 0.0877 300 0.60 18.65 36.210.1341 350 0.70 11.23 40.94 0.1516 400 0.80 −109.15 30.49 0.1129 4500.90 −156.42 22.41 0.0830 EVEN 500 1.00 −414.40 −54.94 −0.2035 OVER 5501.10 −506.10 −89.70 −0.3322 600 1.20 −613.52 −133.89 −0.4959 650 1.30−619.41 −136.31 −0.5049 700 1.40 −624.94 −138.54 −0.5131 750 1.50−625.97 −138.96 −0.5147

Use of a double-sided IDE (i.e., IDE 2) will result in largerdisplacements for the 20 μm piezoelectric as the in-plane E-fields arehigher. Selecting the 20% overlap results as providing a desirablediaphragm displacement.

The limitation to pitch is the high voltage required to maintain theE-field at 3V/μm with increasing inter-electrode spacing. Assuming apractical pitch of 100 μm, 10% electrode duty cycle, and 20% overlap,the optimal piezoelectric thickness is determined by comparing thecomputed diaphragm (−U_(max)) and volume (−ΔV) displacements. In Table2, the optimum thickness for maximum displacement (i.e., 613.52 μm and133.89 pL) is about 20 μm. This result is also shown as the peak ofcurve 148 in FIG. 17, and results in a p/t_(PZT) of 5, although a rangewhere the pitch of the electrodes being 2 to 8 times the thickness ofthe piezoelectric would also provide useful results. TABLE 2 IDE1Optimal Pitch Studies p = 100 μm, dc = 10%, r_(Diap) = 0.5 mm, t_(Diap)= 38 μm, E≈3 V/μm, 20% overlap t_(PZT) −Umax −ΔV (um) t_(PZT)/_(p) (nm)(pL)  5 0.05 263.17 56.62 10 0.1 459.42 99.39 15 0.15 571.06 124.18 200.2 613.52 133.89 25 0.25 610.06 133.29 30 0.3 580.52 126.61 40 0.4492.46 106.12 50 0.5 403.95 85.08 60 0.6 329.45 67.08 70 0.7 269.9152.58 80 0.8 222.84 41.03 90 0.9 185.48 31.87 100  1.0 155.57 24.59

Another characteristic to consider in optimizing the diaphragm structureare the variations of volume displacement due to different underlap andoverlap conditions. FIG. 18 shows the results of this investigation forthe disc and annular ring piezoelectric diaphragm structure. Eachstructure includes a diaphragm having a radius (r_(Diap)) of 500 μm, athickness (t_(Diap)) of 38 μm, and a piezoelectric annular ring with aradius (r_(PZT)), which varies from an underlapping situation (i.e.,less than 1.0) to an overlapping situation (i.e., greater than 1.0), anda thickness (t_(PZT)) of 20 μm. Curve 150 is for a single-sided discdiaphragm structure with an IDE on top of the piezoelectric and curve154 is for a disc diaphragm structure with a double-sided IDEarrangement. The third curve 152 is for an annular ring diaphragmstructure with 100 μm radius piezoelectric portion removed. The curvesindicate that the volume displacements are smaller and positive forunderlap situations, but there is a transition over to larger andnegative displacement for overlap situations, with little change beyond20% overlap for both the disc and annular ring diaphragm structures.

Turning attention to the annular ring design, the optimal inner radiusof the annular ring 49 was determined by varying the annular radius from400 μm to 0 μm. The simulation showed the peak displacement is locatedat an annular radius of 300 μm. TABLE 3 lists results at variousoperational values for different annular radii (_(annulus)). TABLE 3Performance of annular piezoelectric r_(diap) = 500 μm, t_(diap) = 38μm, t_(PZT) = 20 μm, E = 3 V/μm (Cv), P = 2 atm (Cp) r_(annulus) ΔV <um><pL> 400 143.58 300 196.69 200 193.69 100 157.10  0 126.85

Thus, from the foregoing it has been determined for a disc piezoelectricdiaphragm structure, large volume displacements for voltage applied isoptimized in a range of 10% to 30% overlap, and preferably at 20%overlap or a disc radius of 600 μm, covering a 500 μm diaphragm. Volumedisplacements are even larger for annular ring piezoelectric diaphragmstructures; peaking, again, when there is an underlap of the innerradius in a range of 30% to 50%, and preferably 40% (i.e., the innerradius is about 300 μm) and the outer radius is 600 μm (i.e. 20%overlap). Of course, benefits from under and overlapping may be obtainedin other ranges, such as where an inner radius (edge) dimensionunderlaps the diaphragm by approximately 10-50% and the outer radiusedge dimension overlaps the diaphragm by approximately 3-30%.

FIG. 19 shows a simulation of the annular ring diaphragm structure 156optimized with 40% underlap of the inner radius 158 and 20% overlap ofthe outer radius 160.

Turning attention to two-region diaphragm structure 50 of FIGS. 4A, 4Band 7A, 7B, in one embodiment both the annular ring 51 and disc 52 areconfigured for operation in the d₃₁ mode. In this design, one of theregions, for example the disc electrode 54 b, as illustrated in FIG. 7B,will have a positive voltage applied, and the annular ring electrode 54a will have a negative voltage applied relative to common bottomelectrode 54 c. Given uniform poling in a Z-axis, one region willexpand, causing bending in a concave down fashion, and the other regionwill contract causing bending concave upwards. Both of these motionswork together to provide a maximum total deflection. The selection wherethe occurrence of a concave-down versus a concave-up transition exists,is guided by the natural bending modes of the diaphragm and is shown byboundary 53.

The d₃₃ mode of operation makes it is possible for annular ring 51and/or disc 52 to take advantage of the transverse changes in geometryobtained in the d₃₃ mode, which are two to three times larger than thetransverse changes available in the d₃₁ mode, for most piezoelectricmaterials.

Since the selection of boundary 53 between annular ring 51 and discregion 52 does not affect stiffness, a simulation of the deformation ofthe diaphragm under applied pressure will appear the same for alllocations of the boundary. FIG. 20 provides the results of such modelingfor an active diaphragm having a 500 micron radius. A reasonable fit tothe data provides a simple polynomial which can be solved analyticallyto define various features of the system. The radius of inflection inone dimension (R) and the radius which corresponds to the sum of thesecond derivatives (2-D equating to zero (2-D “inflection”, a “saddlepoint” R, and Theta)) 162 is noted in FIG. 20. Alternatively, one maysolve the full analytical expression for deformation and find the samepoint.

Total 2-D inflection radius is the radius (e.g., approximately 0.36)where curvature in the X-axis plus the curvature in the Y-axis is equalto zero. On first inspection, it may be assumed that the optimumboundary location 53 would correspond to the inflection point on the Raxis (1-D). However, the optimum boundary point turns out to be the 2-Dinflection location, as illustrated in FIG. 21 (i.e., for a 1,000 microndiameter, each point is the result of a simulation run, and the optimumis approximately 73%, compared to the 72% from analysis in FIG. 20). Forvoltages applied oppositely to the disc 52 and the annular ring 51 (ontheir tops with respect to the bottom), the piezoelectric tends to curldown in the center and curl up around the edge. The ideal location forthe boundary 53 utilizes this tendency to produce the optimaldisplacement of the diaphragm when voltage is applied.

From a simulation with a typical diaphragm structure, this two-electrode54 a, 54 b design provides an approximate 57% improvement of volumedisplacement versus voltage over an optimal single electrode design(with diameters scaled to give matching C_(p), where C_(p) is volumedisplacement per unit pressure applied). The optimum C_(v) (where C_(v)is the volume displaced per unit volt applied) for a single electrodedesign, with a thickness of material used in this example, is withapproximately 80% coverage of the diaphragm with the piezoelectricmaterial.

In the described structure, increased deflection of the diaphragm occursas compared to a single electrode design, since the contraction andexpansion of the piezoelectric material is matched to the naturalbending mode of the diaphragm. Contraction is initiated in the centralregion when it is desired to have a concave-up position. An expansion ofthe piezoelectric in the central region is used when it is desired tohave a concave-down position (given that the piezoelectric is on top ofthe diaphragm). The overall stiffness pressure per volume displaced(1/C_(p)) is maintained and even improved over conventional singleelectrode construction, and the voltage requirement for actuation isdecreased. Stated alternatively, the volume displaced per unit voltapplied (C_(v)) is increased over single region designs.

In the preceding electrode configuration, annular ring 51 and disc 52 ofdiaphragm structure 50 were driven in the same d_(ij) mode. Thefollowing describes an embodiment where a mixed poling and electricfield arrangement is used for annular ring 51 and disc 52. Particularly,as shown in FIG. 22A-22B, construction of the present embodiment issimilar to that previously described in that there are two regions ofpiezoelectric defined as the annular ring 51 and disc 52, which areconcentric to each other and attached to diaphragm 42.

FIGS. 22A-22B emphasize the two-region design may include configurationswith electrodes on both surfaces of the piezoelectric (i.e., an annularring electrode and disc electrode arrangement on a second surface of thepiezoelectric). More specifically, FIG. 22A depicts a diaphragmstructure 170 with an annular ring electrode 172 and disc electrode 174on a top surface of a piezoelectric (not shown), and an annular ringelectrode 176 and disc electrode 178 on a bottom surface of thepiezoelectric. The top surface electrodes 172 and 174 are provided withpower via a conductor 180, and the bottom side electrodes 178 and 176being provided with power via a conductor 182.

FIG. 22B (which is an enlarged section of FIG. 22A) more clearlyillustrates the diaphragm structure 170 includes a staggered electrodedesign. More specifically, the top annular ring electrode 172 is offsetor staggered from the position of bottom annular ring electrode 176.Similarly, top disc electrode 174 is also not aligned with bottom discelectrode 178. It is to be noted that an alternative embodiment includesthe electrodes in a non-staggered or even arrangement.

With continuing attention to FIGS. 22A-22B, the outer bottom annularring electrode in this embodiment may be designed with a diameter of1.000 mm (1000 microns), the diameter of the upper annular ringelectrode 172 is 0.910 mm (910 microns), the diameter of the lower discelectrode 178 is 0.830 mm (830 microns) and the diameter of the upperdisc electrode 174 is 0.760 mm (760 microns). The distance of staggerbetween the lower annular ring electrode 176 and the upper annular ringelectrode 172 is 0.035 mm (35 microns) It is to be appreciated theforegoing values are representative values which are not intended tolimit the present embodiment, and it is to be understood other sizes andvalues may be used which permit implementation of the disclosedconcepts.

As the entire diaphragm 42 is covered with piezoelectric material in thedesigns of FIGS. 22A-22B, the stiffness of the diaphragm is maintainedover conventional designs, which tend to locate the edge of thepiezoelectric close to the edge of the active diaphragm or somewhatinterior, thereby causing the stiffness to be reduced at the edge of theactive region, and thereby affecting the overall stiffness. This higherstiffness design is particularly beneficial in improving performance influid ejection applications as the resonance frequencies are maintainedat a higher level in these designs.

In the present embodiments, actuation of the annular ring and the discare accomplished by distinct modes of operation. The annular rings arepoled and operated to function in a d₃₃ mode, whereas the disc regionsare configured and operated in a d₃₁ mode.

To achieve these alternate modes of operation, the annular rings arepoled in the R (radial) axis of a cylindrical coordinate system, and thediscs are poled in the Z-axis of a classical right-hand coordinatesystem. In some applications, the vector of poling for the outer region(annular rings) may implement a complex function of position, since thepoling would generally be accomplished by application of the highvoltage to the electrodes of 3 to 15 times the operating voltage (1 to 5times the coercive field strength). The field in the R axis would beestablished by adjustment of the voltages for optimum effect during thepoling. The specific position and adjustment of voltages would vary fromdesign and size of the piezoelectric. Such positioning would, however,upon the teaching of the present application be within the understandingof one of ordinary skill in the art. Therefore, for purposes ofdescriptions herein, the poling is considered to be radial in direction.

Employing this dual electrode design with differing driving conventions,permits multiple driving options. FIGS. 23A-23D are presented toillustrate various ones of these driving options, wherein forconvenience these views show only one edge of annular ring 51 associatedwith disc 52. In particular, when the disc electrode 178 is grounded(i.e., V_(bot1) in the figures), then varying combinations, and valuesof voltages V_(top1), V_(top2), and V_(bot2) may be applied toelectrodes 172, 174 and 176 respectively.

In FIGS. 23A-23D disc portions 52 have been poled to operate in the d₃₁mode, wherein the electric field (E) is applied in a direction oppositethe poled field (P). The annular ring portions 51 are poled in theradial direction (P). However, electrodes 172 and 176 (presented in astaggered configuration) have electric fields applied to alter theirexpansion and/or contraction states. For example, in FIG. 23A, both topelectrode 172 and electrode 176 have E-fields applied to cause topregion and bottom region expansion of the piezoelectric. This isillustrated by showing the arrows coming into the electrodes.

FIG. 23B shows the application of the E-fields which cause a contractionof both the top and bottom of the piezoelectric. This situation isdepicted by showing the arrows extending from electrodes 172 and 176.FIG. 23C illustrates an embodiment where electrode 172 has an E-fieldapplied to cause a top expansion of the piezoelectric, whereas theapplication of an E-field to electrode 176 causes a bottom piezoelectriccontraction. Lastly, in FIG. 23D, the E-field is applied to electrode172 to cause a top portion piezoelectric contraction, whereas theapplication of the E-field to bottom electrode 176 causes a bottomportion piezoelectric expansion.

Turning to FIG. 24, shown is a partial diaphragm structure 190 attachedto an anchor portion 192. In a first state, the diaphragm structure isshown having no voltages applied and is, therefore, in substantially aplanar position. However, upon application of the voltages such as inFIG. 23B, the combination of those voltages provide a deflection of thediaphragm 42 where the center 194 is bending into a spherical shape(i.e., concave downward, which occurs when the diaphragm 42 is deflectedupward). At the same time, the annular ring 51 is bending into acylindrical shape which smoothly joins to the disc 52. The bending inthe center 194 in this situation is caused when the piezoelectricexpands in the plane of the diaphragm 42, which it does when theelectric field is applied in the opposite direction as the polingvector. The outer edge (annular ring) 51 in this case tends to curl intoa cylinder from which best joins to the center 194 when thepiezoelectric in this region is contracting. The voltage applied to theannular rings result in an electric field which is mostly anti-parallelto the poling vector.

The partial view of FIG. 24 is also shown graphically in FIG. 25 whichemphasizes where the voltage penetrates into the piezoelectric, and thatthe largest voltage penetration is at the annular ring.

Turning to FIG. 26, set forth is an outer edge electrode diaphragmdisplacement design where the disc is operated in the d₃₁ mode and theannular ring in the d₃₃ mode. The annular rings electrodes 172, 176 areeven, as opposed to a staggered design. As previously described and asagain shown in FIG. 26, disc 52 of the piezoelectric is poled in theZ-axis, with the electric field (E) applied in an opposite direction.The annular ring 51 has the piezoelectric poled in a radial direction(R) in plane with the material. Thereafter, the various options ofvoltage application shown in FIGS. 23A-23D are applied to theelectrodes.

In connection with the designs of FIGS. 23A-23D and 26, it wasdetermined, by simulation, that the embodiment resulting in the highestusable deflection was provided by the top contraction, bottomcontraction for the non-staggered design of FIG. 26. The generatedvalues for this option are set forth in the third section of thefollowing TABLE 4, which also lists results for a structure such asshown in FIGS. 23A-23D, employing the staggered electrode design. Thetop contraction and bottom contraction combination of the even electrodedesign results in the second greatest deflection (i.e., 566.31 U_(max))for the even electrodes, causing a volume displacement (ΔV) of 190.45pL. This deflection was obtained by applying 60 volts to electrode 64,285 volts to electrode 62, grounding (0 volts) electrode 68, and theapplication of 225 volts to electrode 66. It may be noted that thescenario of applying voltage so as to expand the top and contract thebottom of piezoelectric provides a greater volume displacement (212.81pL). However, the intent of the present deflection scenarios are toapply a voltage such that the field strength in the material ismaximized, but where the voltage does not approach the coercive fieldfor the piezoelectric material at any point.

The simulations undertaken for the present embodiments were targeted toachieve peak fields of 3 volts per micron as a practical value. Withregard to the top expand, bottom contract option for the even electrodedesign, however, this option was simulated with a voltage which exceededthe coercive field in the piezoelectric between the top and bottom outerelectrodes and therefore would be undesirable. Also, while the obtainedvalues for the staggered design in the first section of TABLE 4 aregreater (i.e., 626.67; 624.56) than the non-staggered design, thestaggered design may not be as desirable as the non-staggered design dueto manufacturing issues and the ability to pole properly.

TABLE 4 further provides results of simulations for an outer edgeelectrode (OEE) (annular ring electrode) where the annular rings areequal to each other with a 450 micron radius and have a width of 40 μm.

As may also be determined by a review of TABLE 4, the simulation togenerate this table defined the diaphragm radius (r_(diap)) as being 0.5mm, the radius of the piezoelectric (r_(PZT)) at 0.5 mm, the thicknessof the PZT (t_(PZT)) at 20 μm, the thickness of the diaphragm (t_(diap))at 38 μm and the applied electric field (E) at about 3 V/μm. TABLE 4Comparative PZT Displacements r_(diap) = 0.5 mm, r_(PZT) = 0.5 mm,t_(PZT) = 20 μm, t_(diap) = 38 μm, E ≈ 3 V/μm U_(max) ΔV V_(t1) V_(t2)V_(b1) V_(b2) PZT Cases (nm) (pL) (V) (V) (V) (V) OEE Top expand 125.4053.50 60 −135 0 −225 Stagger Bottom expand Elect Top expand 125.40 53.5060 −135 0 −225 Bottom expand Top contract 626.67 195.42 60 255 0 225Bottom contract Top expand 624.56 218.62 60 −135 0 225 Bottom contractTop contract 127.51 30.30 60 255 0 −225 Bottom expand OEE Top expand158.20 66.67 60 −60 0 −60 Even Bottom expand Elect Top contract 400.23147.81 60 180 0 60 450 Bottom contract w = Top expand 421.63 157.16 60−60 0 60 40 μm Bottom contract Top expand 136.80 57.32 60 180 0 −60Bottom expand OEE Top expand 93.54 45.84 60 −165 0 −225 Even Bottomexpand Elect Top contract 566.31 190.45 60 285 0 225 415 Bottom contractw = Top expand 596.15 212.81 60 −165 0 225 75 μm Bottom contract Topcontract 63.69 23.48 60 285 0 −225 Bottom expand

In FIG. 27, curves 200-206 correspond to top and bottom expansionoptions which were previously discussed in connection with the electrodedesign of FIG. 26, and whose values correspond to the third section ofTABLE 4. As noted here, curve 200 represents an option where theapplication of voltages to the annular electrodes causes top expansionand bottom contraction of the piezoelectric. This results in the largestdeflection curve, whereas the remaining curves 202-206 show lesserdegrees of deflection for their specific application of voltages of theannular ring electrodes.

Thus, disclosed is a radial poling and application of electric fields togenerate a d₃₃ mode of operation for annular rings, in combination withoperation of a disc in a d₃₁ mode. The electrodes on the annular ringare positioned in relationship to each other as in an even or staggeredarrangement. Typical values for bulk ceramic piezoelectric using d₃₃mode are approximately 500 pM per volt, and typical values for bulkceramic piezoelectric using d₃₁ mode are approximately—200 pM per volt.An aspect of the present concepts as directed to drop ejection, is anoptimized usage for multi-sized droplet ejection, which may be achievedby selective application of voltages to the disc and the annular ringelectrodes in alternative combinations to give variable-sized droplets.

The foregoing discussion has primarily focused on unimorph diaphragmstructures. As defined herein, a unimorph diaphragm is one with a singlepiezoelectric. It is to be appreciated, the concepts of the presentapplication may also be used in connection with a bimorph diaphragmstructure 210, such as illustrated in FIG. 28. In this design, insteadof a single piezoelectric, two piezoelectrics 212, 214 are used toactuate diaphragm 216. Piezoelectric 212 is provided with energy viaelectrodes 218 and 220. Whereas piezoelectric 214 is supplied withenergy via electrodes 222 and 224. In this figure, electrodes 222 and224 are shown on a bottom surface of piezoelectric 214. It is to beunderstood that this is simply one embodiment, and these electrodes maybe on a top surface as in other designs. The bimorph piezoelectricelements 212, 214 may also be designed with each piezoelectric elements212 and 214 having electrodes on both upper and bottom surfaces. Thepiezoelectrics may be connected to each other by an adhesive interface226. However, alternatively, and as shown by the dotted line, an inertconductive centerplate 228 may be provided to isolate the twopiezoelectric structures from each other. In one embodiment, thecenterplate may be a stainless steel plate. Piezoelectrics 212,214 maybe configured as discs, annular rings, or a combination thereof, asdisclosed in the preceding discussion.

In the described structures, maximum deflection of the diaphragm occurs,since the contraction and expansion of the piezoelectric material ismatched to the two natural bending regions of the diaphragm. Contractionis initiated when it is desired to have a concave-up bending. Anexpansion of the piezoelectric material is used when it is desired tohave a concave-down bending (given that the piezoelectric material is ontop of the diaphragm). The overall stiffness pressure per volumedisplaced (1/C_(p)) is maintained and even improved over conventionalsingle electrode construction, and the voltage requirements foractuation are decreased. Stated alternatively, the volume displaced perunit volt applied (C_(v)) is increased.

The diaphragm structures described in the preceding paragraphs may beemployed as components in larger devices. In these situations, overtime,poling intensity may diminish, causing a poling drift which will resultin a degradation of the larger devices' operational capabilities. Thispoling drift may occur with any piezoelectric material, but it is knownto be especially detrimental when high response piezoelectrics are used.

To address this situation, described below are system designs, circuitryand poling methodology which permit the poling of the piezoelectricwhile incorporated into the larger device. This poling may be theoriginal poling of the piezoelectric or may be undertaken as a re-polingof the piezoelectric. Thus, the use of the following system, circuit andmethods permit for in-situ poling and re-poling of the piezoelectricused in the diaphragm structures described, as well as other knownpiezoelectric structures. For example, existing diaphragm structureswhich implement a single piezoelectric with a single voltage to causeactuation, may take advantage of the following described systems,circuit and methods.

Turning to FIGS. 29 and 30, the physical structure for the elements ofthis system are depicted in partial views. FIG. 29 shows a bottom sideor lower electrode configuration 230 comprised of electrodes 232(electrodes 233 will be discussed in connection with FIGS. 35A-37) andconductors 234. Bottom side electrode configuration 230 is located on asurface of the device, such as a printhead, to which islands ofpiezoelectric are to be attached. Turning to FIG. 30, a piezoelectricstructure 238 carries a top side or upper electrode configuration 240.The piezoelectric configuration 238 includes a plurality ofpiezoelectric islands 242. The islands are constructed in a way suchthat there are bridges or interconnects 244 which run down the length ofthe column. In this design, the upper side electrode configuration 240is designed to have an inner disc electrode 246 and an annular ringelectrode 248. A conductor 250 connects each of the discs 246 in acolumn together, and a conductor 252 connects each of the annular ringsof a column together. The upper side interconnect 240 is located onpiezoelectric configuration 238, such that the electrodes 246, 248 andconductors 250, 252 do not extend over the edges of islands 242 andinterconnects 244 of piezoelectric structure 238. In full construction,the bottom electrode 230 of FIG. 29 will be located on the opposite sideof piezoelectric structure 238, which carries the top electrodeconfiguration 240. Building top electrode configuration 240 to only beon the top surface of the piezoelectric, and not attempting to step itover the edge of the piezoelectric, allows for the routing of top metalelectrode configuration 240 over the bottom electrode configuration 230.The piezoelectric, in this design, is used as an insulator between thesetwo metal conductors, as the piezoelectric is a dielectric which issubstantially non-conducting.

Turning to FIG. 31, depicted is a printhead 254 which implement theelements of FIGS. 29 and 30 in a two-dimensional array of ejectorcolumns and rows. Conductors 234, 250 and 252 are routed out to the edgeof the two-dimensional array for connection to external drivingelectronics, not shown. These connection lines or conductors may beconnected to the driving electronics via connectors 256. It is to beappreciated that connectors 256 are shown in a generalized manner asbonding pads, and any of a number of known connection techniques may beutilized, such as wire bonding, bump soldering, TAB among others.Additionally, in FIG. 31, while the conductors 234, 250 and 252 areshown connected to connectors 256 at the bottom of the printhead, ifappropriate, connections may be made from all four sides of theprinthead.

Turning to FIG. 32, illustrated is a partial switching circuit 260,which may be formed using conventional electrical fabrication techniquesand is used to control actuation of diaphragm structures, such as thoseof FIG. 31. Switching circuit 260 may include a pulse amplifier 262,which supplies signal to switching array chips 264 used to controlapplication of power to diaphragm structures 266. In this design,conductor 250 is connected to disc electrode 246, and conductor 252 isconnected to annular ring electrode 248. Bottom electrode 232 is on anopposite side of a piezoelectric such as 242 (of FIG. 30) and isconnected to the switching array 264 via the conductor 234. Discconductor 250 connects to each of the discs 246, and annular ringconductor 252 connects to each annular ring 248 of a column as shown inFIGS. 29-31. Voltage supply 268 supplies signals to pulse amplifier 262during normal drop ejection operation of this circuit. However, duringthe poling operation, as pulse amplifier 262 is set to zero volts,voltage supply 268 is essentially out of the circuit. A high voltagesupply 270 supplies power to disc electrode 246, and power supply 272supplies power to annular ring electrode 248.

The voltages required for poling are substantially higher than the pulsevoltages used for printing (about 10-100 volts) and are limited in mostapplications by arcing problems on the face of the printhead. These highvoltages imply a rather high cost per switch if a switch were providedin each line to an ejector. Also, the switches used to set the data tothe printer array are limited in voltage capacity. Knowing theselimitations, the circuit of FIG. 32 may be used to generate a polingcycle in the following sequence.

In a first step, with the system in an on state and the software set tobegin poling operation, all of the data inputs 274 are set to a closedstate, and the pulse amplifier 262 is set to zero (0) volts. In thisstate, the data switches are self-protecting against high voltages,since the current flowing during the poling cycle is low and theswitches are able to sink this low current into the virtual ground ofpulse amplifier 262. Next, the high voltage power supplies 270, 272 areturned on and ramped up to a desired voltage for a set period of timerequired for a particular poling operation. For example, this set timeperiod may be between 1 and 30 minutes, and preferably 15 minutes inmany implementations. Should arcing between points on a surface of theprinthead between the two high voltages becomes an issue, then the powersupplies are turned on one at a time, and the poling undertaken in twoseparate phases. The poling arrangement shown in FIG. 32, with the highvoltage supply 270 set at a positive voltage, and the high voltage powersupply 272 set at a negative voltage will result in distinct polingresults. For example, the disc may be poled in the conventionalright-hand coordinate system in a Z-axis direction (i.e., for operationin a d₃₁ mode), whereas the annular ring portion of the piezoelectricmay be poled using a cylindrical coordinate system, in a radial (R)direction of the piezoelectric material (i.e., for operation in a d₃₃mode).

Next, the high voltage power supplies 270, 272 are then ramped down andturned off. The normal function of pulse amplifier 262 and the switcharrays 264 to emitting fluid drops is then restored.

The impedance of the high voltage supplies, when off or at 0 volts,would be at a low value (roughly less than 0.2 ohms). If required, amechanical relay may be used to short the common point to ground.

By the design shown in FIGS. 29-32, an in-situ poling or re-poling ofpiezoelectric is achieved. This design, also makes it possible to usethe circuit of FIG. 32 to perform both the poling/re-poling operationsand then return to a normal function of operation for emitting selecteddroplets to form a desired pattern.

The described system may be fabricated using a number of manufacturingprocesses. FIG. 33 illustrates a high level process flow 280 showing aprocessing operation for the manufacture and attachment of thepiezoelectric element.

Initially, an array of piezoelectric islands, having the mentionedinterconnects, are fabricated by depositing piezoelectric islands ontoan appropriate substrate by use of a direct marking technology 282.Preferably the substrate is made of sapphire, or other appropriatematerial. In the deposition techniques employed, ceramic type powdersare used in a preferred embodiment. The fabrication process includessintering the material preferably at a temperature of approximately1000° to 1350° C. for densification, although other temperature rangesmay also be used in appropriate circumstances. Following the fabricationprocess the surface of the formed structures of piezoelectric islandsare polished 284, preferably using a dry tape polishing technique. Oncethe piezoelectric islands have been polished and cleaned, electrodes 233as shown in FIG. 29 are deposited on the polished surface of thepiezoelectric islands 286. It should be noted that this bottommetallization is designed to be in intimate contact with thepiezoelectric. This is the reason it is deposited first, prior to thepiezoelectric being attached to the contacting metal on the printhead.The metal on the printhead surface may not otherwise achieve sufficientcontact to the piezoelectric. The formation of the electrodes may alsoor alternatively include known lithographic and/or etching techniques inorder to obtain the desired electrode configurations. Next, the surfaceof the piezoelectric islands with the electrodes are permanently bondedto a final target 288, such as to a substrate or as part of a largersystem. Such substrate may have conductors such as in FIG. 29, whichmake electrical contact to the piezoelectric electrodes 233, as will beshown in more detail in FIGS. 36A-38B. When used as an ejector, thelarger system may be a printhead. It is noted that this operationcompletes the contact to the metal for the bottom interconnection 230(of FIG. 29) of the piezoelectric. Typically, the composition of thepiezoelectric is doped or undoped piezoelectric, but any piezoelectricmaterial, such as lead titanate, lead zirconate, lead magnesium titanateand its solid solutions with lead titanate, lead zinc titanate and itssolid solutions with lead titanate, lithium niobate, lithium tantanate,and others may be used.

At this point, the substrate on which the piezoelectric islands wereinitially deposited is removed through a liftoff process 290 usingradiation energy such as from a laser or other appropriate device. Thereleasing process involves exposure of the piezoelectric elements to aradiation source through the substrate, to break an attachment interfacebetween the substrate and the piezoelectric elements. Additional heatingis implemented, if necessary, to complete removal of the substrate. Oncethe liftoff process has been completed, a removable material is appliedto fill in the areas between the piezoelectric islands attached to theprinthead 292. Thereafter, top surfaces of the newly exposedpiezoelectric islands are polished 294. Next, a second electrodeconfiguration is deposited on a second surface of the piezoelectricmaterial 296. This configuration may be in the form of electrodes 246,248 and conductors 250, 252 of FIG. 30. The electrode configuration maybe formed, including or alternately using lithographic patterning,etching, or via a laser liftoff process. Next excess potting materialand/or photoresist is removed 298. At this point the device, such as aprinthead, is ready for connection to an electric control circuit.

With attention to FIG. 34, which illustrates step 282 in greater detail,piezoelectric elements or islands 242 and interconnects 244 aredeposited on an appropriate substrate 300, and then sintered at 1000° to1350° C. for densification. The depositing step may be achieved by anumber of direct marking processes including screen printing, jetprinting, ballistic aerosol marking (BAM) or acoustic ejection, amongothers. Using these techniques permits flexibility as to the type ofpiezoelectric element configurations. For example, when thepiezoelectric islands and interconnects may be made by screen printing,the screen printing mask (mesh) can be designed to have various shapesor openings resulting in a variety of shapes for the piezoelectricelements, such as rectangular, square, circular or rings, among others.Use of these direct marking techniques also permit generation of veryfine patterns.

The substrate used in the processes of this application will havecertain characteristics, due to the high temperatures involved and—aswill be discussed in greater detail—the fact that the substrate is to betransparent for the liftoff process. Specifically, the substrate is tobe transparent at the wavelengths of radiation beam emitted from theradiation source, and is to be inert at the sintering temperatures so asnot to contaminate the piezoelectric materials. A particularlyappropriate substrate is sapphire. Other potential substrate materialsinclude transparent alumina ceramics, aluminum nitride, magnesium oxide,strontium titanate, quartz, among others. In one embodiment of theprocess, the substrate selected is transparent for a radiation source,such as an excimer laser operating at a wavelength of 308 nm, and doesnot have any requirement on its crystallographic orientation. It ispreferable that the selected substrate material be reusable, which willprovide an economic benefit to the process.

After fabrication of the piezoelectric islands and interconnects hasbeen completed, the process moves to step 284, where the top surface ofthe piezoelectric islands and interconnects polished through a tapepolishing process to remove any surface damage layer, such as due tolead deficiency. This step ensures the quality of the piezoelectricelements and homogenizes the thickness of piezoelectric elements. Byhaving a homogenized thickness, each of the piezoelectric elements of anarray will bond to the final target system or the transfer substrateeven when a very thin epoxy bonding layer or a thin film intermetallictransient liquid phase bonding layer is used.

In one preferred embodiment, the tape polishing step is a dry tapepolishing process that provides a planar flat polish out to the edge ofthe surfaces of the piezoelectric elements, which avoids a crowningeffect on the individual elements. Compared to a wet polishingprocesses, the dry tape polishing does not cause wearing of the edges ofthe piezoelectric elements, making it possible to fabricatehigh-quality, thickness and shape-identical piezoelectric elements. Oncepolishing has been completed, the surface is cleaned, in one instance byapplication of a cleaning substance.

After polishing and cleaning, the process moves to step 286 where, asshown in FIG. 35A, metal electrodes and conductors (e.g., Cr/Ni), whichmay be in the form of electrodes 233 of FIG. 29, are deposited on thesurface of the piezoelectric islands 242 and interconnects 244 bytechniques such as sputtering or evaporation with a shadow mask. Theelectrodes and conductors can also be deposited by a direct markingmethod, such as screen printing, and sintered at suitable temperatures.

Alternatively, when using a thin film intermetallic transient liquidphase bonding process, certain low/high melting-point metal thin filmlayers may be used as the electrodes for the piezoelectric islands, thusin some cases it is not necessary to deposit an extra electrode layersuch as Cr/Ni. However, preferably the thin film intermetallic transientliquid phase bonding process is undertaken after metal electrodedeposition, such as Cr/Ni deposition. This process is generally shown inFIG. 35B, where a thin film layer of high melting-point metal 302 (suchas silver (Ag), gold (Au), Copper (Cu), Palladium (Pd)) and a thin filmlayer of low melting-point metal 304 (such as Indium (In), Tin (Sn)) maybe deposited on the piezoelectric islands and interconnects and a thinlayer of high melting-point metal (such as Ag, Au, Cu, Pd) may bedeposited on the bonding substrate. These materials are then used toform a bond.

Once the electrodes are formed, the piezoelectric islands are thenbonded to the final target substrate or system (step 288 of FIG. 33).For example, as depicted in FIGS. 36A and 36B, the final target could bea metal foil (or the surface of a printhead) 306, which is put on acarrier plate 308 during the process. The bonding is accomplished byusing a nonconductive epoxy layer 310 which can be as thin as less than1 μm. The thin epoxy contains sub-μm conductive particles, which in oneembodiment may be conductive balls (such as Au balls) 312 so the epoxyis conductive in the Z direction (the direction perpendicular to thesurface of metal foil). Thus it can keep the electric contact betweenthe surface electrode of the piezoelectric elements and the metal foil.The concentration of the conductive balls can be controlled in such arange that the cured thin epoxy is conductive in the Z direction but notconductive in the lateral directions, as done for anisotropic conductivefilms. The shrinkage of the epoxy maintains contact between the surfacesand the balls in the Z direction.

In an alternative embodiment shown in FIGS. 36B and 36C, conductiveballs 312 are removed, and bonding is accomplished using thenonconductive epoxy layer 310 alone. As shown in more detail by FIG.36C, electrical contact is maintained via electrical contact points 313,formed when the surface of the electrode 233 and metal foil (orprinthead) are moved into contact, with suitable surface roughness orasperity of the piezoelectric films and/or metal foil (printhead).

In an alternative embodiment, bonding to the final target (e.g.,printhead) may be accomplished by using the previously mentioned thinfilm intermetallic transient liquid phase bonding, employing in oneembodiment a high melting-point metal (such as Ag, Cu, Pd, Au, etc.)/lowmelting-point metal (such as In, Sn) intermetallic compound bondinglayer or alloy 314, FIG. 37.

More particularly, for thin film intermetallic transient liquid phasemetal bonding, a high melting-point metal thin layer, such as a Pd thinlayer, is deposited on the target substrate or system. Next thepiezoelectric configuration consisting of islands 242 and electrode 233(patterned on the islands) is moved into contact with the Pd thin layerand heated under pressure above the melting point of the lowmelting-point metal, e.g., about 200° C. By this operation the highmelting-point metal/low melting-point metal/high melting-point metalcombination, such as Pd/In/Pd layer (a high melting-point metal/lowmelting-point metal such as Pd/In layer previously deposited on thepiezoelectric islands 242 as shown in FIG. 35B) will form the highmelting-point metal-low melting-point metal bonding layer compound oralloy 314. This compound or alloy may be a PdIn₃ alloy layer which isabout 1 μm-thick, which acts to bond piezoelectric islands 242 andtarget substrate (i.e., printhead) 306. Functionally, the lowmelting-point metal diffuses into the high melting-point metal to formthe compound/alloy.

As the melting point of the formed intermetallic compound phase can bemuch higher than that of the low melting-point metal, the workingtemperature of the bonding layer can be much higher than the temperatureused to form the bonding. For example, when Indium (In) is used as thelow melting-point metal and Palladium (Pd) is used as the highmelting-point metal, the bonding can be finished below or at 200° C. asthe melting point of In is about 156° C. However, the workingtemperature of the formed intermetallic compound bonding layer, PdIn₃,can be well above 200° C. because the melting point of PdIn₃ is about664° C. The thickness of the bonding layer could be from 1 to 10 μm, buta thinner bonding layer (e.g., about 1 μm) is expected for this purpose.Further, the amount of high and low melting-point metals can becontrolled so they will be totally consumed to form the intermetallicbonding layer.

The next step is to release the piezoelectric islands 242 andinterconnects 244 from substrate 300. The releasing of substrate 300 maybe accomplished by a liftoff operation as depicted in FIGS. 38A and 38B.The following description is based on the arrangement of FIG. 36A.However, it is equally applicable to all provided alternatives.Substrate 300 is first exposed to a radiation beam (such as a laserbeam) from a radiation source (such as an excimer laser source) 316,having a wavelength at which the substrate 300 is substantiallytransparent. In this way a high percentage of the radiation beam passesthrough the substrate 300 to the interface of the substrate and islands242 and interconnects 244 at the surface of the substrate. The energy atthe interface acts to break down the physical attachment between thesecomponents. Following operation of the radiation exposure, and as shownin FIG. 38B, heat is applied by a heater 318. While the temperatureprovided by the heater will vary depending on the situation, in oneembodiment a temperature of between 40 to 50° C. is sufficient toprovide easy detachment of any remaining contacts to fully release thepiezoelectric islands 242 and interconnects 244 from substrate 300.Desirably, the substrate is of a material that allows it to be re-usedafter a cleaning of its surface.

In one embodiment, the radiation source is an excimer laser source. Thewavelength used in this situation is about 308 nm, and the piezoelectricmaterial is polycrystalline and was screen printed on substrates andtherefore more weakly bound to the substrate compared to the epitaxiallygrown single crystal films.

Exposure to the radiation source does raise the potential of damage tothe surface of the piezoelectric elements, this potential damage shouldhowever be no more than to a thickness of about 0.1 μm. Since thethickness of the piezoelectric elements, in most embodiments, will belarger than 10 μm, the effect of the surface damage layer can beignored. However, if otherwise necessary or when piezoelectric elementsof less than 10 μm are formed by these processes, any surface damagelayer can be removed by appropriate processes including ion milling ortape polishing. It is to be appreciated FIGS. 38A and 38B are simplyused as examples, and the described liftoff process may take place usingalternatively described arrangements. Also, for convenience, FIGS. 38Aand 38B corresponds to the structure of FIG. 36A. However, the sametypes of procedures may be applied to other relevant arrangements inaccord with the present teachings.

Next, and following the steps for adding potting material and polishing,as depicted in FIGS. 39A and 39B, second side surface electrodes andconductors, such as disc electrodes 246 and annular ring electrodes 248and corresponding conductors 250, 252, are deposited on the releasedsurfaces of islands 242 and interconnects 244 with a shadow mask or byother appropriate method in accordance with step 296 of FIG. 33.

For the case where a piezoelectric islands are already bonded to thefinal target substrate or system such as by the process of FIG. 33, thepotting material and/or photoresist is removed and the process iscomplete. At this point, the printhead is now ready for attachment to anelectrical circuit (i.e., via wire bonding, bump techniques or by othermeans). If the bump processing techniques are used, those appropriatemanufacturing processes would be undertaken.

Turning to FIG. 40, illustrated is an alternative high-level processflow 320. This process differs from that of FIG. 33 in that the bondingis to a transfer substrate rather than to a final target substrate orsystem (e.g., the printhead). A benefit of bonding first to a transfersubstrate is that it allows the structure to be tested prior to apermanent attachment to an expensive device. Thus, the fabrication step322, the tape polishing step 324 and the electrode depositing step 326are performed in the same manner as steps 282, 284 and 286 of FIG. 33.At bonding step 328, the bonding is to a transfer substrate, as thisconnection is not intended to be permanent. Thereafter, the liftoff step330, the addition of potting material 332, the second polishing step334, the second electrode deposition step 336 and the removal of thepotting material 338, which correlate to steps 290-298 of FIG. 33, areperformed.

The piezoelectric elements are then bonded to a final target substrateor system 340, in a procedure similar in design to step 288 of FIG. 33.Following bonding step 340, the transfer substrate is removed 342. Whenbonding to a final target substrate or system, a thin high strengthbonding layer is used to minimize or avoid undesirable mechanicaldamping or energy absorption of the bonding layer. This bonding will,however, also permit maintaining of electrical contact between the metalelectrodes on the piezoelectric elements and the final target substrateor system or a conductive surface of the final target substrate orsystem.

Employing the process of FIG. 40, the configured actuator may be poledand then tested, prior to the final bonding in step 340. In this wayonly fully operational devices will be bonded to final target substratesor systems, thus avoiding yield loss of the target substrates orsystems.

Thus, the foregoing has described a system, circuit and method where aninterconnect technique uses traces of metal which run on a top surfaceof the piezoelectric, together with traces which run under thepiezoelectric to make a completed interconnection. This constructionallows for crossovers where the bottom metal is overlayed withpiezoelectric, and the top interconnect where needed. The overallcircuit utilizes both sides of the piezoelectric actively and isconstructed in a way to minimize costs. This design avoids buildingswitches into the connections on the switch array side of thepiezoelectric elements, and avoids keeping one surface of thepiezoelectric connected constantly to ground.

The description of the dual-use switching circuit has been described inthe FIGURES with reference to a single bottom electrode for eachcorresponding piezoelectric island, and two electrodes in the form of adisc and annular ring on a top surface of each piezoelectric island. Itis again to be appreciated that the present design may be used whereonly a single electrode is used on a top surface. Further, the describedsystem may be used where multiple electrodes (more than two) are locatedon both the top and bottom surfaces of the piezoelectric islands. Insituations where multiple electrodes are employed on each surface of thepiezoelectric islands, to avoid undesirable crossover additional stepsto isolate the conductors of the additional electrodes may be required.In one instance, this isolation may be achieved by etching a smallchannel or depression into the piezoelectric material itself, or into asubstrate which may carry the electrodes. Thereafter a conductor for oneof the electrodes is deposited, and the channel is covered with an oxideor other insulating material which would permit a further conductor topass over the lower covered conductor.

This arrangement permits for the poling and in-situ re-poling of thepiezoelectric material as needed to maintain performance over the lifeof the larger device, such as a printer. Particularly, present dayprinters may suffer a droop in poling magnitude of up to ten percentover the life of the product, and some degree of nonuniformity ofprinting results will occur. It is expected the piezoelectric in adevice as described herein may be in the 20 to 30 micron range comparedto the existing 100 micron range in use today. This thinner material, ifnot repoled when necessary, will cause even larger droop rates. It is tobe understood the re-poling operation may be undertaken at preset timeintervals as coded by software. Alternatively, a user may institutere-poling by depressing a button provided on a machine for that purpose.

As previously noted, while this present discussion shows theinterconnections running out of a single edge, i.e., the bottom, it ispossible for the interconnections to be designed for connection at boththe top and bottom, or even at all four sides of a printhead. Analternative to running the interconnections to the outer edges of theprinthead is for the top metallization layer to directly bond thismaterial to the surface using a two-dimensional array technique, such asball grid arrays or silver paste bumps to a flex circuit.

While the exemplary embodiment has been described with respect tospecific embodiments by way of illustration, many modifications andchanges will occur to those skilled in the art. It is, therefore, to beunderstood that the appended claims are intended to cover all suchmodifications and changes as fall within the scope and spirit of theexemplary embodiment.

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 22. A method of fabricating an array ofmulti-electroded piezoelectric transducers for use by a printhead havingin-situ poling capabilities, comprising: carrying a piezoelectricconfiguration on a substrate used for high temperature annealing, thepiezoelectric configuration, including (i) a plurality of piezoelectricislands formed in a two-dimensional array, each island including a firstside and a second side, each of the first sides in contact with thesubstrate, and (ii) piezoelectric island interconnects which extend downlengths of each column of the piezoelectric islands; polishing thesecond side of the piezoelectric islands substantially flat; forming abottom metal layer onto at least portions of the second sides of thepiezoelectric islands and interconnects, the bottom metal layer havingfirst areas corresponding to the piezoelectric islands and second areascorresponding to the piezoelectric interconnects; positioning aprinthead metal actuation layer to receive the second sides of thepiezoelectric islands and interconnects; bonding the metalized secondside of the piezoelectric islands and interconnects to the printheadmetal actuation layer; removing the substrate from the first side of thepiezoelectric islands and interconnects; polishing the first side of thepiezoelectric islands and interconnects; forming an upper metal layeronto at least portions of the first side of the piezoelectric islandsand interconnects, wherein the upper metal layer includes first areascorresponding to the piezoelectric islands and second areas which arecorresponding to the piezoelectric interconnects; and positioning thesecond areas of upper and bottom metal layers for connection toprinthead electronics by printhead connectors.
 23. The method of claim22, wherein the printhead connectors have smaller widths than thepiezoelectric interconnects.
 24. The method of claim 22, wherein thepiezoelectric is in a form of an annular ring being at least somedistance from a center of a diaphragm.
 25. The method of claim 22,wherein the poling voltages for in-situ poling are greater than about300V.
 26. The method of claim 22, wherein drop ejection voltages of theprinthead are in the range of 10-100 volts.
 27. The method of claim 22,wherein the poling time for in-situ poling is between approximately 1minute and 30 minutes.
 28. The method of claim 22, further includingdiscs on the piezoelectric islands and connecting each disc in a columntogether by a first conductor.
 29. The method of claim 22, furtherincluding locating annular rings on the piezoelectric islands andconnecting each annular ring in a column together by a second conductor.30. The method of claim 22, further including building the top electrodeconfiguration to only be on a top surface of the piezoelectric.
 31. Themethod of claim 22, wherein the piezoelectric is used as an insulatorbetween the first and second conductors.
 32. A method of fabricating anarray of multi-electroded piezoelectric transducers comprising: carryinga piezoelectric configuration on a substrate, the piezoelectricconfiguration, including (i) a plurality of piezoelectric islands, eachisland including a first side and a second side, each of the first sidesin contact with the substrate, and (ii) piezoelectric islandinterconnects which extend down lengths of each column of thepiezoelectric islands; forming a bottom metal layer onto at leastportions of the second sides of the piezoelectric islands andinterconnects, the bottom metal layer having first areas correspondingto the piezoelectric islands and second areas corresponding to thepiezoelectric interconnects; positioning a metal actuation layer toreceive the second sides of the piezoelectric islands and interconnects;bonding the metalized second side of the piezoelectric islands andinterconnects to the metal actuation layer; removing the substrate fromthe first side of the piezoelectric islands and interconnects; andforming an upper metal layer onto at least portions of the first side ofthe piezoelectric islands and interconnects.
 33. The method of claim 32,further including discs on the piezoelectric islands and connecting eachdisc in a column together by a first conductor.
 34. The method of claim32, further including locating annular rings on the piezoelectricislands and connecting each annular ring in a column together by asecond conductor.
 35. The method of claim 32, further including buildingthe top electrode configuration to only be on a top surface of thepiezoelectric.
 36. The method of claim 32, wherein the piezoelectric isused as an insulator between the first and second conductors.
 37. Amethod of fabricating an array of multi-electroded piezoelectrictransducers for use by a printhead having in-situ poling capabilities,comprising: carrying a piezoelectric configuration on a substrate usedfor high temperature annealing, the piezoelectric configuration,including (i) a plurality of piezoelectric islands formed in atwo-dimensional array, each island including a first side and a secondside, each of the first sides in contact with the substrate, and (ii)piezoelectric island interconnects which extend down lengths of eachcolumn of the piezoelectric islands; forming a bottom metal layer ontoat least portions of the second sides of the piezoelectric islands andinterconnects, the bottom metal layer having first areas correspondingto the piezoelectric islands and second areas corresponding to thepiezoelectric interconnects; positioning a printhead metal actuationlayer to receive the second sides of the piezoelectric islands andinterconnects; bonding the metalized second side of the piezoelectricislands and interconnects to the printhead metal actuation layer;removing the substrate from the first side of the piezoelectric islandsand interconnects; forming an upper metal layer onto at least portionsof the first side of the piezoelectric islands and interconnects,wherein the upper metal layer includes first areas corresponding to thepiezoelectric islands and second areas which are corresponding to thepiezoelectric interconnects; and positioning the second areas of upperand bottom metal layers for connection to printhead electronics byprinthead connectors.
 38. The method of claim 37, further includingdiscs on the piezoelectric islands and connecting each disc in a columntogether by a first conductor.
 39. The method of claim 37, furtherincluding locating annular rings on the piezoelectric islands andconnecting each annular ring in a column together by a second conductor.40. The method of claim 37, further including building the top electrodeconfiguration to only be on a top surface of the piezoelectric.
 41. Themethod of claim 37, wherein the piezoelectric is used as an insulatorbetween the first and second conductors.